Recent discoveries indicate 1) that schistosomiasis in Malaysia is caused by a new species of schistosome closely related to S. japonicum and S. mekongi, 2) that snails of the Tribe Triculini (Pomatiopsidae: Triculinae) may host a number of undescribed S. japonicum-like schistosomes, 3) that Triculini snails are generally highly endemic and 4) that undescribed Triculini species probably exist in the mountainous regions of Malaysia and western Thailand. My proposal is designed to provide information on various strains and species of S. japonicum-like schistosomes and their triculine snail hosts in Malaysia and Thailand. The objectives of this proposal are 1) to describe the mammalian schistosome recently discovered in Malaysia, 2) to define the habitat and range of its Triculini snail host, 3) to identify its reservoir host(s), 4) to carry out expeditions in Malaysia and Thailand designed to discover new S. japonicum-like schistosomes and their snail hosts, and 5) to determine if snails closely related to the natural host of the "Malaysian" schistosome and S. mekongi are suitable hosts for these schistosomes. In addition to routine morphological and life history comparisons, multivariate analysis, allometry and scaling will be used to determine the relationships among S. mekongi, S. japonicum, and the schistosomes described in this study.